The present study is a cross-validation of the Validity-10 embedded symptom validity indicator from the Neurobehavioral Symptom Inventory (NSI) for the detection of questionable response validity during evaluation for mild traumatic brain injury (TBI). The sample and data derived from a three-site Veterans Affairs (VA) parent study to validate the TBI Clinical Reminder, a routine set of questions asked of all recently returned veterans at VA facilities to screen for history of TBI. In the parent study, veterans recently returned from Iraq and Afghanistan underwent an evaluation for TBI with a physician and completed an assessment battery including neuropsychological tests of cognitive performance and indicators of symptom and performance validity, psychiatric assessment measures, a structured interview for post-traumatic stress disorder (PTSD), and various behavioral health questionnaires. The present study estimated the test operating characteristics of Validity-10, using NSI results gathered during the physician evaluation to compute Validity-10 scores, and using results on several other measures of symptom and performance validity from the assessment battery as criteria for questionable response validity. Only individuals who had positive screen results for TBI on the TBI Clinical Reminder prior to full evaluation were included in the present sample. Sensitivity of Validity-10 to questionable validity was moderately high (.60 - .70) to excellent (.90 - 1.00) at high levels of specificity (> .80). Effects of different base rates of and different criteria for questionable validity on the utility of Validity-10 were explored as well. Chi-square analyses to determine the effect of PTSD symptoms on the utility of Validity-10 demonstrated overall classification accuracy in general, and false positive rate in particular, were relatively poorer when used with individuals who reported significant PTSD symptoms. Overall, these findings support the use of Validity-10 (at cut score Validity-10 ≥ 19) to identify those veterans being evaluation for mild TBI in the VA system who should be referred for comprehensive secondary evaluation by a clinical neuropsychologist using multiple forms of symptom and performance validity testing. Further studies of the effects of PTSD symptoms on the accuracy of Validity-10 for this purpose are recommended.